Reusable medical, pharmaceutical, and biological instruments are generally sterilized before each use. Additionally, reusable containers employed in medical, pharmaceutical, and biological applications, such as glove boxes and incubators, are generally sterilized before each use. In facilities and applications where these types of instruments and containers are used several times a day, it is important to achieve sterilization efficiently and economically.
Several different methods have been developed for delivering a vapor phase sterilant to an enclosure or chamber for sterilizing the load (e.g., medical instruments) or interior thereof. In one option, the "deep vacuum" approach, a deep vacuum is used to pull liquid sterilant into a heated vaporizer; once vaporized, the sterilant is propelled by its vapor pressure into an evacuated and sealed chamber. In another option, the "flow-through" approach, vaporized sterilant is mixed with a flow of carrier gas that serves to deliver the sterilant into, through and out of the chamber, which may be at slightly negative or positive pressure.
In addition, methods have been developed for optimizing vapor phase sterilization in a deep vacuum and/or flow-through system. U.S. Pat. No. 4,956,145 discloses a deep vacuum method of vapor phase sterilization in which a predetermined concentration of hydrogen peroxide sterilant is maintained in an evacuated, sealed chamber. The amount of sterilant injected into the chamber is regulated or adjusted to account for the decomposition of hydrogen peroxide sterilant vapor into water and oxygen in the closed system over time. A different approach is disclosed in U.S. Pat. Nos. 5,445,792 and 5,508,009, incorporated by reference herein, wherein a predetermined percent saturation is maintained in an open, flow-through sterilization. The rate of hydrogen peroxide vapor injection into a carrier gas is regulated or adjusted in response to predetermined characteristics of the carrier gas.
Also, several systems and apparatus have been developed for conducting vapor phase sterilization. An open flow-through system designed to handle the disposition of residual sterilant vapors is disclosed in U.S. Pat. No. 4,909,999 and is incorporated by reference herein. That system can be integrally associated with or releasably connected to a sealable container.
U.S. Pat. No. 5,173,258, which is incorporated by reference herein, discloses another flow-through system in which vapor phase hydrogen peroxide is introduced into a recirculating, closed flow of carrier gas. The hydrogen peroxide vapor is introduced and maintained at a predetermined concentration selected to optimize the sterilization cycle. The system includes a dryer to dehumidify the recirculating flow, preferably to at least about 10% relative humidity, and thereby prevent moisture build-up resulting from the decomposition of hydrogen peroxide vapor over time. By eliminating moisture build-up, the system can maintain the sterilization chamber at higher concentrations of vapor phase hydrogen peroxide sterilant for longer periods of time (i.e., the predried gas will accept more of the sterilant vapor). Further, to avoid condensation of the sterilant, the relative humidity in the chamber is preferably reduced (e.g., to at least about 10%) prior to introducing sterilant vapor. After decontamination is complete, the enclosure may be rehumidified or conditioned if desired for the selected application.
The foregoing methods and systems are effective at sterilization and/or provide an enhanced sterilization cycle. However, each of the aforementioned flow-through systems employ a comparatively low carrier gas or air flow rate of approximately 12-20 standard cubic feet per minute (SCFM) and a low liquid sterilant injection rate into the vaporizer. If higher carrier gas flow rates of up to 40-70 SCFM or more are employed, an increase in the amount of liquid sterilant injected into the vaporizer is required to maintain a predetermined vapor concentration. The combination of increased liquid and increased flow rate may have the result that not all of the liquid particles come into contact with the heated vaporizer wall and the liquid is not completely vaporized. Further, when employing a vapor sterilant that is easily decomposed by heat, such as hydrogen peroxide vapor, early-formed vapor may be decomposed by the constant heat of vaporizer as it follows a tortuous path through the vaporizer.
Previous low flow rate systems utilized one heater (of one wattage) to preheat the carrier gas prior to its entering the vaporizer. However, when higher air flow rates and higher sterilant injection rates are employed, one heater of one wattage is not sufficient to provide enough heat to the air stream. Furthermore, it may be desirable to provide a wide range of different air flow rates, each requiring a different heating wattage.
Other problems arise when flow-through systems with a high rate of flow are used to decontaminate rigid-walled chambers or enclosures, in which a slightly positive or slightly negative pressure must be maintained, because minute changes in the carrier gas flow rate, produced by adjusting the flow with high velocity blower motors, can be magnified into gross changes in the enclosure pressure, which may exceed process limits or harm processes going on inside the enclosure.
There exists, therefore, a need for further improvements in decontamination systems to accommodate high rates of carrier gas flow-through.